Broomall climate

Broomall Frost Dates and Growing Season

NOAA 1991-2020 normals for Norristown, 14.3 km from Broomall, elevation 62 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Norristown. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 8 and the first fall freeze around October 31, a growing season of about 203 days.

Median at 36°F
last April 22, first October 20
Median at 32°F
last April 8, first October 31
Median at 28°F
last March 31, first November 10

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 9May 3Apr 29Apr 25Apr 22Apr 19Apr 16Apr 11Apr 6
32°FApr 23Apr 18Apr 15Apr 12Apr 8Apr 6Apr 3Apr 1Mar 28
28°FApr 12Apr 7Apr 4Apr 2Mar 31Mar 28Mar 24Mar 20Mar 15
24°FApr 3Mar 30Mar 27Mar 23Mar 19Mar 16Mar 12Mar 8Mar 2
20°FMar 25Mar 20Mar 15Mar 12Mar 8Mar 5Mar 2Feb 26Feb 19
16°FMar 14Mar 8Mar 4Mar 1Feb 26Feb 21Feb 16Feb 11Feb 5

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 6Oct 10Oct 13Oct 16Oct 20Oct 23Oct 27Oct 31Nov 3
32°FOct 14Oct 20Oct 25Oct 28Oct 31Nov 2Nov 4Nov 7Nov 12
28°FOct 27Nov 1Nov 4Nov 7Nov 10Nov 13Nov 15Nov 18Nov 22
24°FNov 7Nov 12Nov 16Nov 18Nov 21Nov 24Nov 28Dec 2Dec 8
20°FNov 18Nov 24Nov 29Dec 1Dec 5Dec 11Dec 17Dec 23Jan 1
16°FDec 1Dec 8Dec 17Dec 22Dec 27Dec 31Jan 3Jan 8Jan 16

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F201194189184180176171166159
32°F222216211207203199195190183
28°F246238233228224220216212206
24°F271263258254249244240234227
20°F299290283277273267262256247
16°F325316309304300295289282274

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
4,869
Cooling degree days, base 65°F
1,254
Growing degree days, base 40°F
6,256
Growing degree days, base 45°F
4,959
Growing degree days, base 50°F
3,815
Growing degree days, base 55°F
2,825
Growing degree days, base 60°F
1,971

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,01802
February86505
March718031
April37015158
May12779420
June13253690
July0394859
August1338801
September42156564
October28320228
November572050
December85908

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 14.3 km from Broomall. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00366370 (Norristown). Public domain.